I have four Mobiblu cube players. Two black ones stopped functioning after working for some time. They do not come when connected to power or PC. They show up only under my computer's device manager as unknown devices. When I connected one of them a message read "player device class." I do have the disk for the players but it doesn't seem to help. The pink one functions but with difficulty, that is the buttons don't always function properly.While it comes on it won't always play tracks. However, if I push buttons repeatedly , sometimes it will play. My newest one is orange and works wonderfully so far. Can anyone offer advice on repairs or where to look? Thank you